Stylus and sensor controller

ABSTRACT

A stylus capable of bidirectionally communicating with a sensor controller includes a receiver that receives an uplink signal sent by the sensor controller, a controller that determines whether a signal having a predetermined waveform is to be continuously sent over a second time period or to be continuously sent over a first time period longer than the second time period, on the basis of the uplink signal, and a transmitter that continuously sends the signal having the predetermined waveform over the first time period or the second time period on the basis of the result of determination by the controller. As a result, the sensor controller can detect a burst signal from the stylus over a wide range in a sensor touch surface, to thereby reduce the possibility that the sensor controller may fail to detect the burst signal.

BACKGROUND Technical Field

The present disclosure relates to a stylus and a sensor controller, andmore particularly to a stylus and a sensor controller that form aposition detecting system in which the sensor controller detects thestylus based on a burst signal sent from the stylus.

Description of the Related Art

Heretofore, a stylus sends, to a sensor controller, a burst signal fordetecting the stylus and its position as well as a data signal includingdata indicative of a pen pressure and a stylus ID. The burst signal is asignal having a predetermined waveform (e.g., an unmodulated signalhaving a predetermined frequency) that is known in advance between thestylus and the sensor controller. The data signal is a signal modulatedwith data to be sent. FIG. 7 of Patent Document 1 discloses an exampleof a stylus that sends such signals.

When the sensor controller has not yet detected the stylus, the sensorcontroller performs a detecting operation by successively using all of aplurality of electrodes arrayed on a touch surface, trying to detect theburst signal. If the sensor controller detects the burst signal as aresult, the sensor controller uses only some of the electrodes that arepositioned in the vicinity of the electrode that has detected the burstsignal, trying to detect the data signal.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: PCT Patent Publication No. WO2015/111159

BRIEF SUMMARY Technical Problems

The conventional sensor controller faces a challenge in that when thestylus has not yet contacted the touch surface (in hover state),sometimes the sensor controller fails to detect the burst signal eventhough the burst signal has reached the touch surface. This is becausethe stylus in hover state is distanced from the touch surface, reducingthe amplitude of the burst signal detected by the sensor controller toan extent that sufficient signal/noise (S/N) ratio cannot be achieved.One way of obtaining a sufficient S/N ratio even when the stylus is inhover state would be to increase the period of a detecting operation perelectrode. However, the increased period of a detecting operation perelectrode makes it difficult to detect the burst signal over a widerange in the touch surface. Then, before all the electrodes in the rangecan be scanned, the transmission of the burst signal may end.

Furthermore, even when a pen-down operation is performed in which thestylus and the sensor controller approach each other at a distance thatprovides a sufficient S/N ratio, if the stylus is sending the datasignal rather than the burst signal at this timing, then there is apossibility that the sensor controller may fail to detect the stylus.

An aspect of the present disclosure is to provide a stylus and a sensorcontroller that maintain a state in which the sensor controller candetect a burst signal over a wide range in a touch surface in order toidentify the position of the stylus that has not been detected, tothereby reduce the possibility that the sensor controller may fail todetect the burst signal.

Technical Solution

According to an aspect of the present disclosure, a stylus capable ofbidirectionally communicating with a sensor controller includes areceiver that receives an uplink signal sent by the sensor controller, acontroller that determines whether a signal having a predeterminedwaveform is to be continuously sent over a second time period or to becontinuously sent over a first time period longer than the second timeperiod, on the basis of the uplink signal, and a transmitter thatcontinuously sends the signal having the predetermined waveform over thefirst time period or the second time period on the basis of the resultof determination by the controller.

According to another aspect of the present disclosure, a stylus capableof bidirectionally communicating with a sensor controller includes areceiver that receives an uplink signal sent by the sensor controller, acontroller that determines a state of the sensor controller based on theuplink signal, and a transmitter that continuously sends a signal havinga predetermined pattern that is known in advance between the stylus andthe sensor controller over a predetermined time period in response to acommand from the controller if the uplink signal indicates that thesensor controller has not detected the stylus. The transmittercontinuously sends a data signal that varies depending on an operationstate of the stylus, rather than continuously sending the signal havingthe predetermined pattern over the predetermined time period, if theuplink signal indicates that the sensor controller has derived theposition of the stylus.

According to an aspect of the present disclosure, a sensor controllercapable of deriving the position of a stylus by detecting a signal sentfrom the stylus is arranged to carry out a step of determining whetherthe stylus has not been detected or has been detected, a step of, if itis determined that the stylus has been detected, sending a second uplinksignal for instructing the stylus to continuously transmit a signalhaving a predetermined waveform over a second time period, and a stepof, if it is determined that the stylus has not been detected, sending afirst uplink signal for instructing the stylus to continuously transmitthe signal having the predetermined waveform over a first time periodlonger than the second time period.

According to another aspect of the present disclosure, a sensorcontroller connected to an electrode matrix of M first electrodesextending in a first direction and N second electrodes extending in asecond direction different from the first direction is arranged to carryout a finger touch detecting step of supplying a predetermined signalrespectively to the M first electrodes and detecting a finger touchbased on the predetermined signal detected respectively by the N secondelectrodes, a full-range scanning step of detecting an undetected stylusand deriving positional coordinates of the stylus using at least part ofthe M first electrodes and at least part of the N second electrodes, anda sector scanning step of deriving positional coordinates of a detectedstylus using fewer first electrodes than the first electrodes used inthe full-range scanning step and fewer second electrodes than the secondelectrodes used in the full-range scanning step.

Advantageous Effects

According to the present disclosure, in a stylus undetected state wherethe possibility that the stylus is hovering is high, the sensorcontroller can expect the stylus to send a long burst signal whichcontinues for a longer period of time than a normal burst signal.Consequently, while the time period of the detecting operation perlinear electrode is made longer than when a normal burst signal isreceived, it is possible to scan more electrodes within the time periodof continuous transmission of a long burst signal, for the purpose ofdetecting a burst signal. The possibility that the sensor controller mayfail to detect a burst signal can be reduced, while ensuring that thesensor controller is capable of detecting a burst signal over a widerange in a touch surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram depicting an arrangement of an electronic device 3according to an embodiment of the present disclosure. FIG. 1(a) depictsa mode of operation of the electronic device 3 for detecting a touch bya finger F, and FIG. 1(b) depicts a mode of operation of the electronicdevice 3 for detecting a stylus 2.

FIG. 2 is a diagram depicting an arrangement of the electronic device 3according to the embodiment of the present disclosure.

FIG. 3 is a diagram depicting configurations of a long burst signal, aburst signal, and a data signal that are sent by the stylus 2 accordingto the embodiment of the present disclosure.

FIG. 4 is a diagram depicting sequences of signals sent and receivedbetween the stylus 2 and a sensor controller 31 when the stylus 2 isabove an uplink detection height AH. FIG. 4(a) depicts the sequence inwhich the sensor controller 31 sends a pen trigger signal, and FIG. 4(b)depicts the sequence in which the sensor controller 31 requests that along burst signal be sent.

FIG. 5 is a diagram depicting sequences of signals sent and receivedbetween the stylus 2 and the sensor controller 31 when the stylus 2 iswithin a sensing range SR and the sensor controller 31 has not yetidentified the position of the stylus 2. FIG. 5(a) depicts the sequencein which the sensor controller 31 sends a pen trigger signal, FIG. 5(b)depicts the sequence in which the sensor controller 31 receives a longburst signal sent by the stylus 2, using linear electrodes 30Y, and FIG.5(c) depicts the sequence in which the sensor controller 31 receives along burst signal sent by the stylus 2, using linear electrodes 30X.

FIG. 6 is a diagram depicting a sequence of signals sent and receivedbetween the stylus 2 and the sensor controller 31 when the stylus 2 iswithin the sensing range SR and after the sensor controller 31 hasidentified the position of the stylus 2. FIG. 6 depicts the sequence inwhich the stylus 2 sends a burst signal and a data signal in hoverstate.

FIG. 7 is a diagram illustrative of the manner in which the sensorcontroller 31 according to the embodiment of the present disclosureoperates. FIG. 7(a) depicts a first half of a full-range scanningprocess, FIG. 7(b) depicts a second (latter) half of the full-rangescanning process, and FIG. 7(c) depicts a sector scanning process.

FIG. 8 is a diagram depicting an arrangement of the stylus 2 accordingto the embodiment of the present disclosure.

FIG. 9 is a flowchart of an overall operation sequence of the sensorcontroller 31 according to the embodiment of the present disclosure.

FIG. 10 is a flowchart of a stylus detecting process carried out by thesensor controller 31 according to the embodiment of the presentdisclosure.

FIG. 11 is a flowchart of an operation sequence of the stylus 2 whichcorresponds to FIG. 10.

FIG. 12 is a diagram depicting an arrangement of a stylus 2 according toa first modification of the embodiment of the present disclosure.

FIG. 13 is a flowchart of an operation sequence of a stylus 2 accordingto a second modification of the embodiment of the present disclosure.

FIG. 14 is a flowchart of an operation sequence of a sensor controller31 according to a third modification of the embodiment of the presentdisclosure.

FIG. 15 is a diagram depicting a long burst signal sent by a stylus 2according to a fourth modification of the embodiment of the presentdisclosure.

FIG. 16 is a flowchart of an operation sequence of a stylus 2 accordingto a fifth modification of the embodiment of the present disclosure.

FIG. 17 is a diagram illustrative of a specific position excludingprocess according to a sixth modification of the embodiment of thepresent disclosure. FIG. 17(a) depicts finger touch areas detected by afinger touch detecting process, and FIG. 17(b) depicts positions of astylus 2 derived by a stylus detecting process carried out immediatelyafter the finger touch detecting process in FIG. 17(a).

FIG. 18 is a flowchart of an operation sequence of a sensor controller31 according to the sixth modification of the embodiment of the presentdisclosure.

DETAILED DESCRIPTION

An embodiment of the present disclosure will be described in detailbelow with reference to the accompanying drawings.

FIG. 1 is a diagram depicting an arrangement of an electronic device 3according to the present embodiment. The electronic device 3 is acomputer having a touch surface such as a tablet terminal, for example,and includes a sensor 30 and a sensor controller 31, as depicted in FIG.1.

The sensor 30 includes a matrix of electrodes including M linearelectrodes 30X (first electrodes) and N (N<M) linear electrodes 30Y(second electrodes) that are disposed inside the touch surface.According to a specific example, M=72, N=46. The M linear electrodes 30Xextend at equal intervals in a first direction parallel to the touchsurface. The N linear electrodes 30Y extend at equal intervals in asecond direction parallel to the touch surface and perpendicular to thefirst direction. The linear electrodes 30X and the linear electrodes 30Yare respectively connected to the sensor controller 31.

The sensor controller 31 detects, via the sensor 30, a touch by a fingerF (also deriving positional coordinates of finger F on the touchsurface) and detects, via the sensor 30, the stylus 2 (also derivingpositional coordinates of the stylus 2 on the touch surface), in atime-division manner.

FIG. 1(a) depicts a mode of operation of the electronic device 3 fordetecting a touch by finger F. As depicted in FIG. 1(a), for detecting atouch by finger F, the sensor controller 31 supplies the linearelectrodes 30Y successively with a predetermined signal (hereinafterreferred to as “finger detecting signal”) and successively scanspotentials of the linear electrodes 30X to detect the finger detectingsignal that has reached the linear electrodes 30X through theintersections of the linear electrodes 30X and 30Y. The amplitude of thefinger detecting signal detected in this manner is smaller when finger Fis close to the intersection, through which the finger detecting signalpasses, than when finger F is not close to the intersection. This isbecause part of the electric current that flows through the linearelectrodes 30X and 30Y flows toward the human body via a capacitivecoupling between finger F and the linear electrodes 30X and 30Y. Thesensor controller 31 detects a touch by finger F by detecting thischange in the amplitude.

FIG. 1(b) depicts a basic mode of operation of the electronic device 3for detecting the stylus 2. As depicted in FIG. 1(b), in the basic modeof operation for detecting the stylus 2, the sensor controller 31performs a detecting operation on a signal (hereinafter referred to as“downlink signal”) sent by the stylus 2, using the linear electrodes 30Xand 30Y successively as reception electrodes. The sensor controller 31detects the stylus 2 based on the detected downlink signal. In actualoperation, there is a situation in which the sensor controller 31detects the stylus 2 using only some of the linear electrodes 30X and30Y. Such situation will be described later.

In order for the sensor controller 31 to detect the stylus 2, it isnecessary for the stylus 2 to be sufficiently close to the touch surfaceof the electronic device 3 so that the sensor controller 31 can receivethe downlink signal. A sensing range SR that is illustrated in FIG. 1(b)is a schematic representation of a range in which the sensor controller31 can receive the downlink signal. When the stylus 2 enters the sensingrange SR, the sensor controller 31 detects the downlink signal, therebydetecting the stylus 2. The movement of the stylus 2 from outside thesensing range SR into the sensing range SR will hereinafter be referredto as “pen-down.” The pen-down is usually performed by an action of theuser to bring the stylus 2 closer to the touch surface of the electronicdevice 3. The state in which the stylus 2 is not yet in contact with thetouch surface though it has entered the sensing range SR is referred toas “hovering.” When the stylus 2 has come into a hovering state based onpen-down, the sensor controller 31 tries to detect the stylus 2 bydetecting a downlink signal. However, while the stylus 2 is hovering,there is a certain distance between the stylus 2 and the touch surface,and depending on the distance, it may be difficult to maintain asufficient S/N ratio, sometimes resulting in a failure to detect thestylus 2. Even when the stylus 2 is in the sensing range SR, the sensorcontroller 31 may sometimes fail to detect the stylus 2 during a periodin which the stylus 2 is sending a data signal rather than a burstsignal. One of the aspects of the present disclosure is to avoid suchfailure.

Here, even when the stylus 2 is outside the sensing range SR, there areinstances in which the stylus 2 is able to receive signals (hereinafterreferred to as “uplink signals”) that the sensor controller 31 has sentto the stylus 2. This is because some uplink signals (a pen triggersignal, a command signal for instructing the stylus 2 to send a longburst signal, etc. to be described later) are sent using the touchsurface in its entirety (all of the linear electrodes 30X or all of thelinear electrodes 30Y or both of them). An uplink detection height AHthat is also illustrated represents a limitation on the height (distancefrom the touch surface) up to which the stylus 2 can receive thoseuplink signals. The uplink detection height AH is at a position higher(a position farther away) from the touch surface than the upper limit ofthe sensing range SR.

FIG. 2 is a diagram depicting an arrangement of the electronic device 3according to the present embodiment. The linear electrodes 30X and thelinear electrodes 30Y of the sensor 30 form capacitive coupling with thestylus 2 and with finger F. When finger F approaches the sensor 30, partof an electric current flowing from the sensor controller 31 to thelinear electrodes 30Y is drawn into finger F through the capacitivecoupling. Since the amplitude of the finger detecting signal detected bythe linear electrodes 30X is now reduced, as described above, the sensorcontroller 31 is able to detect a touch by finger F. The sensor 30 isarranged to be able to send and receive signals bidirectionally to andfrom the stylus 2 through the capacitive coupling.

As depicted in FIG. 2, the sensor controller 31 includes a transmitter60, a selector 40, a receiver 50, a logic unit 70, and a micro computingunit (MCU) 80.

The transmitter 60 is a circuit that generates a finger detecting signalat the timing to detect a touch by finger F, and generates uplinksignals at the timing to detect the stylus 2. The uplink signals includea pen trigger signal that lets the stylus 2 know the existence of thesensor controller 31 and a command signal representing a command for thestylus 2.

FIG. 2 illustrates in detail the transmitter 60 as having functionalblocks related to the generation of uplink signals. The functionalblocks include a pattern supply 61, a switch 62, a spreading processor63, a code train holder 64, and a transmission guard 65. In the presentembodiment, the pattern supply 61 will be described as included in thetransmitter 60. However, the pattern supply 61 may be included in theMCU 80.

The pen trigger signal includes a repetition of a predetermineddetection pattern c1 and a predetermined delimiter pattern STP at theend.

The detection pattern c1 is a pattern of symbol values used for thestylus 2 to detect the existence of the sensor controller 31, and isknown to the stylus 2 in advance (before the stylus 2 detects the sensorcontroller 31). A symbol is a unit of information used for modulation ina transmission process (a unit of information represented by atransmission signal), and a unit of information obtained by demodulatingone symbol as a reception signal in a reception process. The symbolvalues may include a value that is converted into a bit train by thestylus 2 having received a symbol (hereinafter referred to as “bit traincorrelated value”) and a value that is not converted into a bit train(hereinafter referred to as “bit train uncorrelated value”). Accordingto a specific example, the detection pattern c1 includes a pattern “PM”made up of two (2) bit train uncorrelated values “P” and “M.”

The delimiter pattern STP is a pattern of symbol values for notifyingthe stylus 2 of the end of the repetition period of the detectionpattern c1, and includes a pattern that does not appear in therepetition of the detection pattern c1. The delimiter pattern STP isalso known to the stylus 2 in advance (before the stylus 2 detects thesensor controller 31). According to an example, if the detection patternc1 includes a pattern “PM” made up of two bit train uncorrelated values“P” and “M,” as described above, then the delimiter pattern STP mayinclude a pattern “PP” made up of two consecutive bit train uncorrelatedvalues “P.” The delimiter pattern STP and the detection pattern c1 maybe switched around such that the delimiter pattern STP includes apattern “PM” and the detection pattern c1 includes a pattern “PP.”

The pattern supply 61 holds the detection pattern c1 and the delimiterpattern STP, and outputs these patterns in a predetermined order inaccordance with the instruction of a control signal ctrl_t1 suppliedfrom the logic unit 70. Specifically, the pattern supply 61 repeatedlyoutputs the detection pattern c1 in succession during a predeterminedsuccessive transmission period, and outputs the delimiter pattern STPimmediately after the successive transmission period is finished. Inthis manner, the pen trigger signal is sent. The delimiter pattern STPmay be output at the beginning of a command signal indicating aninstruction to send a long burst signal (to be described later).

The switch 62 has a function to select either the pattern supply 61 orthe MCU 80 based on a control signal ctrl_t2 supplied from the logicunit 70, and supply an output signal from the selected one to thespreading processor 63. If the switch 62 selects the pattern supply 61,then the spreading processor 63 is supplied with the detection patternc1 or the delimiter pattern STP from the pattern supply 61. If theswitch 62 selects the MCU 80, then the spreading processor 63 issupplied with control information c2 from the MCU 80.

The control information c2 includes information representing aninstruction (command) for the stylus 2, and is generated by the MCU 80.The command signal described above includes the control information c2.The control information c2 is different from the detection pattern c1and the delimiter pattern STP in that it includes symbol values (forexample, 0 through 15) correlated to a variable-length bit train andthese values are not shared with the stylus 2 in advance.

The code train holder 64 has a function to generate and hold a spreadcode PN of a predetermined chip length having autocorrelationcharacteristics on the basis of a control signal ctrl_t3 supplied fromthe logic unit 70. The spread code PN held by the code train holder 64is supplied to the spreading processor 63.

The spreading processor 63 has a function to obtain a transmission chiptrain having a predetermined chip length by modulating the spread codePN held by the code train holder 64 on the basis of the symbol values(the detection pattern c1, the delimiter pattern STP, or the controlinformation c2) supplied via the switch 62. The spreading processor 63supplies the acquired transmission chip train to the transmission guard65.

The transmission guard 65 has a function to insert a guard period (aperiod in which neither transmission nor reception is carried out) thatis required to switch between a transmission operation and a receptionoperation, between a transmission period for uplink signals and areception period for downlink signals, on the basis of a control signalctrl_t4 supplied from the logic unit 70.

The receiver 50 is a circuit that receives a finger detecting signalsent by the transmitter 60 or downlink signals sent by the stylus 2 onthe basis of a control signal ctrl_r from the logic unit 70.Specifically, the receiver 50 includes an amplifying circuit 51, adetecting circuit 52, and an analog-to-digital (AD) converter 53.

The amplifying circuit 51 amplifies and outputs a signal (a fingerdetecting signal or downlink signals) supplied from the selector 40. Thedetecting circuit 52 is a circuit that generates a voltage commensuratewith the level of an output signal from the amplifying circuit 51. TheAD converter 53 is a circuit that generates a digital signal by samplingthe voltage output from the detecting circuit 52 at predetermined timeintervals. The digital signal output by the AD converter 53 is suppliedto the MCU 80.

The selector 40 includes switches 44 x and 44 y and conductor selectingcircuits 41 x and 41 y.

The switches 44 x and 44 y include one-circuit two-contact switchelements, where a common terminal is selectively connected to either oneof T terminal and R terminal. The common terminal of the switch 44 x isconnected to the conductor selecting circuit 41 x, T terminal of theswitch 44 x is connected to the output terminal of the transmitter 60,and R terminal of the switch 44 x is connected to the input terminal ofthe receiver 50. The common terminal of the switch 44 y is connected tothe conductor selecting circuit 41 y, T terminal thereof is connected tothe output terminal of the transmitter 60, and R terminal thereof isconnected to the input terminal of the receiver 50.

The conductor selecting circuit 41 x is a switch element for connectingthe M linear electrodes 30X selectively to the common terminal of theswitch 44 x. The conductor selecting circuit 41 x is arranged to becapable of connecting some or all of the M linear electrodes 30Xsimultaneously to the common terminal of the switch 44 x.

The conductor selecting circuit 41 y is a switch element for connectingthe N linear electrodes 30Y selectively to the common terminal of theswitch 44 y. The conductor selecting circuit 41 y is arranged to be ableto connect some or all of the N linear electrodes 30Y simultaneously tothe common terminal of the switch 44 y.

The selector 40 is supplied with four control signals sTRx, sTRy, selX,and selY from the logic unit 70. Specifically, the control signal sTRxis supplied to the switch 44 x, the control signal sTRy to the switch 44y, the control signal selX to the conductor selecting circuit 41 x, andthe control signal selY to the conductor selecting circuit 41 y. Thelogic unit 70 controls the selector 40 using these control signals sTRx,sTRy, selX, and selY to send and receive a finger detecting signal, senduplink signals including a pen trigger signal and a command signal, andreceive downlink signals. The controlling of the selector 40 by thelogic unit 70 will be described in greater detail later.

The logic unit 70 and the MCU 80 serve as a controller that controls thetransmitter 60, the receiver 50, and the selector 40 to thereby controltransmission and reception operation of the sensor controller 31.Specifically, the MCU 80 includes a microprocessor that has a read-onlymemory (ROM) and a random-access memory (RAM) therein and operatesaccording to predetermined programs. The logic unit 70 is arranged tooutput control signals described above under the control of the MCU 80.The MCU 80 is arranged to perform a process of deriving coordinate datax and y indicating the position of finger F or the stylus 2 on the basisof a digital signal supplied from the AD converter 53 and outputting thederived coordinate data x and y to a system controller of the electronicdevice 3, and, if the digital signal supplied from the AD converter 53represents a data signal, a process of acquiring data Res represented bythe digital signal and outputting the acquired data Res to the systemcontroller of the electronic device 3.

The controlling of the selector 40 by the logic unit 70 will bedescribed in specific detail below.

For sending and receiving a finger detecting signal, the logic unit 70controls the selector 40 using the control signals sTRx, sTRy, selX, andselY so that N linear electrodes 30Y are successively connected to theoutput terminal of the transmitter 60 and the M linear electrodes 30Xare successively connected to the input terminal of the receiver 50. Asdepicted in FIG. 1, it is possible to supply a finger detecting signalsuccessively to the N linear electrodes 30Y and detect, with thereceiver 50, the finger detecting signal that has come to the linearelectrodes 30X through the intersections of the linear electrodes 30Xand 30Y, thereby detecting a touch by finger F.

For sending uplink signals and receiving downlink signals, the logicunit 70 performs different processes depending on the manner in whichthe stylus 2 is detected and the types of downlink signals. The types ofdownlink signals and sequences of signals sent and received between thestylus 2 and the sensor controller 31 will first be described below, andthen the manner in which the logic unit 70 operates to send uplinksignals and receive downlink signals will be described in detail.

FIG. 3 is a diagram depicting the types of downlink signals sent by thestylus 2 according to the embodiment of the present disclosure. Asdepicted in FIG. 3, the downlink signals include a long burst signal, aburst signal, and a data signal. The long burst signal includes a signalhaving a predetermined waveform as a predetermined pattern known inadvance between the stylus 2 and the sensor controller 31, the signalbeing sent in succession over a predetermined time period T1 (first timeperiod). The burst signal includes the above signal having thepredetermined waveform, sent in succession over a predetermined timeperiod T2 (second time period) shorter than the time period T1. The datasignal includes a data signal generated by modulating the above signalhaving the predetermined waveform with data. Typically, the data signalis sent subsequently to the burst signal over a time periodcorresponding to the difference, T1−T2, between the time period T2 andthe time period T1. It should be noted that a predetermined gap signal(not depicted) for delimiting the burst signal is inserted at thebeginning of the burst signal. The types of the downlink signals to besent by the stylus 2 are selected according to the instruction ofcommand signals sent by the sensor controller 31.

FIGS. 4 through 6 are diagrams depicting sequences of signals sent andreceived between the stylus 2 and the sensor controller 31. FIG. 4depicts the sequences when the stylus 2 is above the uplink detectionheight AH, FIG. 5 depicts the sequences when the stylus 2 is within thesensing range SR and the sensor controller 31 has not yet identified theposition of the stylus 2, and FIG. 6 depicts the sequence when thestylus 2 is within the sensing range SR and the sensor controller 31 hasidentified the position of the stylus 2. These sequences will berespectively described below.

<When the Stylus 2 is above the Uplink Detection Height AH>

FIG. 4(a) depicts the sequence in which the sensor controller 31 sends apen trigger signal and FIG. 4(b) depicts the sequence in which thesensor controller 31 requests that a long burst signal be sent.

As depicted in FIG. 4(a), the sensor controller 31 sends a pen triggersignal over a time period T (=t1−t0) from time t0 to time t1. The sensorcontroller 31 sends the pen trigger signal when it has not yet detectedthe stylus 2. As described above, the pen trigger signal includes arepetition of a predetermined detection pattern c1 and a predetermineddelimiter pattern STP at the end. The stylus 2 intermittently performs adetecting operation to detect the detection pattern c1 by intermittentlyperforming a detecting operation to detect the symbols (“P” and “M” inthe above example) of the detection pattern c1. If the stylus 2 is abovethe uplink detection height AH, then it cannot detect the detectionpattern c1 with its detecting operation. Therefore, the stylus 2 simplyrepeats the detecting operation to detect the detection pattern c1.

As depicted in FIG. 4(b), subsequently to the transmission of the pentrigger signal, the sensor controller 31 starts sending a command signal(denoted by “CMD” in FIGS. 4 through 6) at time t2 subsequent to timet1. The time period required to send the command signal is T0, which isshorter than the time period T. When the sensor controller 31 has notyet detected the stylus 2, the sensor controller 31 sends the commandsignal that instructs the stylus 2 to send a long burst signal. However,the stylus 2 which is above the uplink detection height AH is unable toreceive the command signal and does not send a long burst signal inresponse to the command signal, but simply repeats the detectingoperation to detect the detection pattern c1.

After the sensor controller 31 has sent the command signal thatinstructs the stylus 2 to send a long burst signal, the sensorcontroller 31 performs a detecting operation to detect a long burstsignal. This detecting operation corresponds to a first half of afull-range scanning process to be described later, and is carried outusing the N linear electrodes 30Y in succession. Details of thefull-range scanning process will be described later. Since the stylus 2does not send a long burst signal at this time, the sensor controller 31does not detect a long burst signal. The time period that can be usedfor the detecting operation to detect a long burst signal is T1 (T−T0)corresponding to the difference between the time period T and the timeperiod T0. When the detecting operation to detect a long burst signal isperformed using the N linear electrodes 30Y in succession, the detectingoperation of the long burst signal is temporarily completed at time t3prior to time t4 (=t2+T) at which the time period T1 elapses. The sensorcontroller 31 that has not detected a long burst signal during thedetecting operation enters a sleep mode from time t3 to time t4. Thesensor controller 31 thus has its electric power consumption reduced.After time t4, the transmission of a pen trigger signal is repeated.

<When the Stylus 2 is within the Sensing Range SR and the SensorController 31 has not yet Identified the Position of the Stylus>

FIG. 5(a) depicts the sequence in which the sensor controller 31 sends apen trigger signal, FIG. 5(b) depicts the sequence in which the sensorcontroller 31 receives a long burst signal sent by the stylus 2, usinglinear electrodes 30Y, and FIG. 5(c) depicts the sequence in which thesensor controller 31 receives a long burst signal sent by the stylus 2,using linear electrodes 30X.

As depicted in FIG. 5(a), when a pen-down movement is made (time t6),the stylus 2 can detect the detection pattern c1 in its subsequentdetecting operation (time t7) to detect the detection pattern c1. Havingdetected the detection pattern c1, the stylus 2 continues the detectingoperation until a delimiter pattern STP is detected. When the delimiterpattern STP is detected, the stylus 2 synchronizes with the sensorcontroller 31 on the basis of the detection time. The synchronization iscarried out by the generation of a transmission and reception scheduleto be specifically described later.

FIG. 5(a) depicts an example in which a pen-down movement is made attime t6 between time t5 at which a pen trigger signal starts being sentand time t8 (=t5+T) at which the pen trigger signal ends being sent, andthe stylus 2 detects the detection pattern c1 at time t7 prior to timet8. The same process is carried out even if a pen-down movement is made(e.g., at time t6′ depicted in FIG. 5(b)) while the sensor controller 31is performing a detecting operation to detect a long burst signal,except that the timing for the stylus 2 to detect the detection patternc1 is slightly delayed.

Then, as depicted in FIG. 5(b), when the sensor controller 31 startssending a command signal for instructing the stylus 2 to send a longburst signal at time t9 after time t8, the stylus 2 receives the commandsignal and continuously sends a long burst signal over a time period T1until time t10 (=t9+T). The sensor controller 31 detects the stylus 2 bydetecting the long burst signal thus sent.

Specifically, as depicted in FIG. 5(b), the sensor controller 31 usesthe N linear electrodes 30Y in succession to perform a detectingoperation to detect a long burst signal (a first half of a full-rangescanning process to be described later). At this time, since a longburst signal is detected with either one or more of the linearelectrodes 30Y, the sensor controller 31 stores the detected intensityof the long burst signal at each of the linear electrodes 30Y. Then, asdepicted in FIG. 5(c), the sensor controller 31 again starts to send acommand signal for instructing the stylus 2 to send a long burst signalat time t11 after time t10, and again performs a detecting operation todetect a long burst signal from the end of the transmission of thecommand signal. This detecting operation is carried out using the Mlinear electrodes 30X in succession until time t12 (=t11+T) (a latterhalf of a full-range scanning process to be described later). Since along burst signal is detected with either one or more of the linearelectrodes 30X in this detecting operation, the sensor controller 31stores the detected intensity of the long burst signal at each of thelinear electrodes 30X. The sensor controller 31 then derives thepositional coordinates of the stylus 2 on the touch surface on the basisof the previously stored detected intensity of the long burst signal ateach of the linear electrodes 30Y and the presently stored detectedintensity of the long burst signal at each of the linear electrodes 30X.

<When the Stylus 2 is within the Sensing Range SR and after the SensorController 31 has Identified the Position of the Stylus 2>

FIG. 6 depicts the sequence in which the stylus 2 sends a burst signaland a data signal. As depicted in FIG. 6, the sensor controller 31 thathas identified the position of the stylus 2 starts sending a commandsignal for instructing the stylus 2 to send data at subsequent time t13.In response to the command signal, the stylus 2 continuously sends aburst signal over time period T2. The sensor controller 31 detects theburst signal, and derives positional coordinates of the stylus 2 on thebasis of the detected burst signal. The detecting operation to detectthe burst signal is carried out successively using only those of the Mlinear electrodes 30X and the N linear electrodes 30Y which areindicated as being in the vicinity of the stylus 2 by the positionalcoordinates of the stylus 2 that have been derived at the last time(sector scanning process to be described later). The stylus 2 sends adata signal including data that it has been instructed to send,subsequently to the burst signal. The sensor controller 31 receives thedata signal and decodes the data signal to acquire the data sent by thestylus 2. The reception of the data signal is carried out using only onelinear electrode 30X or linear electrode 30Y that corresponds to thepositional coordinates of the stylus 2 that have been derived at thelast time.

Referring back to FIG. 2, operation of the logic unit 70 at the time ofdetecting the stylus 2 and performing bidirectional communication withthe stylus 2 will be described in detail below with reference to FIG. 2.

For sending a pen trigger signal and a command signal for instructingthe stylus 2 to send a long burst signal (FIGS. 4(a) and 4(b) and FIGS.5(a), 5(b) and 5(c)), the logic unit 70 controls the selector 40 to useall of the M linear electrodes 30X or all of the N linear electrodes 30Yor both of them simultaneously. Specifically, the logic unit 70 controlsthe selector 40 with the control signals sTRx, sTRy, selX, and selY sothat the output terminal of the transmitter 60 is connected to the Mlinear electrodes 30X or the N linear electrodes 30Y or both. Therefore,a pen trigger signal and a command signal for instructing the stylus 2to send a long burst signal are sent using the touch surface in itsentirety, thereby allowing the stylus 2 to receive these signals nomatter where it may be located in the sensing range SR depicted in FIG.1.

For receiving a long burst signal when the stylus 2 has not yet beendetected (FIG. 4(b) and FIG. 5(b)), the logic unit 70 controls theselector 40 to use the N linear electrodes 30Y in succession, asdepicted in FIG. 4(b) and FIG. 5(b). Specifically, the logic unit 70controls the selector 40 using the control signals sTRy and selY toconnect the N linear electrodes 30Y successively to the input terminalof the receiver 50. The sensor controller 31 can thus receive a longburst signal sent by the stylus 2, thereby detecting the stylus 2 nomatter where it may be located in the sensing range SR depicted in FIG.1.

FIG. 7(a) is a diagram illustrative of the manner in which the sensorcontroller 31 operates in such a case. As depicted in FIG. 7(a), thesensor controller 31 successively scans the N linear electrodes 30Y. Thesensor controller 31 does not scan the M linear electrodes 30X at thistime because it is possible to scan the entire surface of the sensor 30using only the N linear electrodes 30Y and, in addition, in order toincrease the scanning time period per electrode.

For receiving a long burst signal when positional coordinates of thestylus 2 have not yet been derived after having detected the stylus 2 byreceiving a long burst signal (FIG. 5(c)), the logic unit 70 controlsthe selector 40 to use the M linear electrodes 30X in succession, asdepicted in FIG. 5(c). Specifically, the logic unit 70 controls theselector 40 using the control signals sTRx and selX to connect the Mlinear electrodes 30X successively to the input terminal of the receiver50. The sensor controller 31 derives positional coordinates of thestylus 2 on the touch surface in the manner described above on the basisof the results of the control of the selector 40 and the previousdetection of the long burst signal with the N linear electrodes 30Y.

FIG. 7(b) is a diagram illustrative of the manner in which the sensorcontroller 31 operates in such a case. As depicted in FIG. 7(b), thesensor controller 31 successively scans the M linear electrodes 30X. Inthe present description, the scanning process that successively uses theN linear electrodes 30Y as depicted in FIG. 7(a) (first half) and thescanning process that successively uses the M linear electrodes 30X asdepicted in FIG. 7(b) (latter half) are combined together into a processreferred to as “full-range scanning process.”

For sending a command signal after having derived positional coordinatesof the stylus 2 (FIG. 6), the logic unit 70 controls the selector 40 touse only those of the M linear electrodes 30X and the N linearelectrodes 30Y which are in the vicinity of the stylus 2. Specifically,if the stylus 2 is positioned at the intersection of the (j+5)th linearelectrode 30X and the (i+5)th linear electrode 30Y, for example, thenthe logic unit 70 controls the selector 40 using the control signalssTRx, sTRy, selX, and selY so that five linear electrodes, for example,on each of both sides of the intersection, i.e., the jth to (j+10)thlinear electrodes 30X and the ith to (i+10)th linear electrodes 30Y, aresimultaneously connected to the output terminal of the transmitter 60.Since the sensor controller 31 can now send a command signal using onlythose linear electrodes in the vicinity of the stylus 2, the electricpower consumption required to send a command signal is reduced. If thepalm of a hand or the like placed on the touch surface is supplied witha command signal, then the ground potential supplied to the stylus 2 mayincrease, possibly resulting in a reduction in the accuracy with whichthe stylus 2 detects an uplink signal. However, inasmuch the sensorcontroller 31 sends a command signal using only those linear electrodesin the vicinity of the stylus 2, as described above, the possibilitythat the palm of a hand or the like will be supplied with a commandsignal is low, and hence the accuracy with which the stylus 2 detects anuplink signal is prevented from being reduced.

For receiving a normal burst signal rather than a long burst signalafter having derived positional coordinates of the stylus 2 (FIG. 6),the logic unit 70 controls the selector 40 to use only those of the Mlinear electrodes 30X and the N linear electrodes 30Y which are in thevicinity of the stylus 2. Specifically, if the stylus 2 is positioned atthe intersection of the (j+5)th linear electrode 30X and the (i+5)thlinear electrode 30Y, for example, then the logic unit 70 controls theselector 40 using the control signals sTRx, sTRy, selX, and selY so thatfive linear electrodes, for example, as depicted in FIG. 6, on each ofboth sides of the intersection, i.e., the jth to (j+10)th linearelectrodes 30X and the ith to (i+10)th linear electrodes 30Y, aresuccessively connected to the input terminal of the receiver 50. Sincethe reception time period per linear electrode is thus increased, it ispossible to receive a burst signal reliably.

FIG. 7(c) is a diagram illustrative of the manner in which the sensorcontroller 31 operates in such a case. In this example, it is assumedthat the stylus 2 is positioned at the intersection of the (j+5)thlinear electrode 30X and the (i+5)th linear electrode 30Y. The sensorcontroller 31 successively scans only 11 linear electrodes 30X rangingfrom the jth to (j+10)th linear electrodes 30X and 11 linear electrodes30Y ranging from the ith to (i+10)th linear electrodes 30Y, among theM×N linear electrodes, and derives positional coordinates of the stylus2 on the basis of the results of the scanning process. The scanningprocess in which both of some of the M linear electrodes X and some ofthe N linear electrodes Y are used to re-derive (update) positionalcoordinates of the stylus 2 that have been derived once is referred toas “sector scanning process.”

For receiving a data signal (FIG. 6), the logic unit 70 controls theselector 40 to use only one linear electrode 30X or linear electrode 30Ycorresponding to the position of the stylus 2 derived from the lastburst signal. Specifically, the logic unit 70 controls the selector 40using the control signals sTRx, sTRy, selX, and selY so that one linearelectrode 30X or linear electrode 30Y is connected to the input terminalof the receiver 50. It is possible to utilize the data signaltransmission time period (=T1−T2) to the fullest in order to send datafrom the stylus 2 to the sensor controller 31.

The operation of the logic unit 70 for detecting the stylus 2 andperforming bidirectional communication with the stylus 2 has beendescribed above.

FIG. 8 is a block diagram depicting functional blocks of the stylus 2according to the present embodiment. As depicted in FIG. 8, the stylus 2includes an electrode 21, a pen pressure detection sensor 23, and asignal processor 24.

The electrode 21 is a conductive member provided adjacent to the distalend of a core body of the stylus 2. The electrode 21 serves as anantenna for sending downlink signals and also as an antenna forreceiving uplink signals sent from the sensor controller 31 via thecapacitive coupling.

The pen pressure detection sensor 23 is a pressure sensor that detects apressure (pen pressure) applied to the distal end of the core body ofthe stylus 2.

The signal processor 24 has a function to receive uplink signals fromthe sensor controller 31 via the electrode 21, perform processingsequences depending on the contents of the received uplink signals,generate downlink signals to be sent to the sensor controller 31, andsend the generated downlink signals to the sensor controller 31 via theelectrode 21. Specifically, the signal processor 24 functionallyincludes a switch 76, a receiver 71, a transmitter 75, and a controller90. These functional blocks will be described below in order.

The switch 76 includes a one-circuit two-contact switch element where acommon terminal is selectively connected to either one of T terminal andR terminal. The common terminal of the switch 76 is connected to theelectrode 21, T terminal thereof is connected to the output terminal ofthe transmitter 75, and R terminal thereof is connected to the inputterminal of the receiver 71. The state of the switch 76 is controlled bycontrol signals SWC from the controller 90. For receiving uplink signalsfrom the sensor controller 31, the controller 90 controls the switch 76with the control signal SWC so that R terminal and the common terminalare connected to each other. For sending downlink signals to the sensorcontroller 31, the controller 90 controls the switch 76 with the controlsignal SWC so that T terminal and the common terminal are connected toeach other. In an initial state, i.e., during a period until the stylus2 detects the detection pattern c1 described above, the controller 90controls the switch 76 to keep R terminal and the common terminalconnected to each other, and then enters a sleep mode for reducing theelectric power consumed by the stylus 2.

The receiver 71 is a circuit that receives a signal supplied from theswitch 76 (a signal that has arrived at the electrode 21) and decodesthe symbol values contained in the received signal, and includes awaveform regenerator 71 a and a correlation operator 71 b. The receiver71 is arranged to be able to detect a detection pattern c1, a delimiterpattern STP, and control information c2 described above by decoding thesymbol values. Until the receiver 71 detects a detection pattern c1, itperforms its reception operation only intermittently in order to reducethe electric power consumed by the stylus 2.

The waveform regenerator 71 a binarizes the level of an electric charge(voltage) induced in the electrode 21 with a clock that is several times(e.g., four times) the chip rate of the spread code PN described above,shapes the binarized level into a binary train (chip train) havingpositive and negative polarity values, and outputs the chip train. Thecorrelation operator 71 b stores the chip train output from the waveformregenerator 71 a into a register, performs a correlation operation onthe chip train while successively shifting it with the above clock withrespect to the spread code PN (or a code produced by inverting and/orcyclically shifting the spread code PN), thereby decoding the symbolvalues contained in the received signal.

The receiver 71 sequentially determines whether the symbol valuesdecoded by the correlation operator 71 b represent the detection patternc1 or not. If the receiver 71 detects the detection pattern c1 as aresult, then the receiver 71 detects the existence of the sensorcontroller 31 and issues a trigger signal EN to the controller 90, whichmakes it possible for the controller 90 to perform a process dependingon the command indicated by the command signal.

When the receiver 71 has detected the detection pattern c1, it switchesfrom the intermittent reception operation to a continuous receptionoperation, and sequentially determines whether the decoded symbol valuesrepresent the delimiter pattern STP or not. If the receiver 71 detectsthe delimiter pattern STP as a result, then the receiver 71 outputsdetection time t2 to the controller 90.

After having detected the delimiter pattern STP, the receiver 71performs a reception operation to receive a command signal sent by thesensor controller 31 according to a schedule (to be described later)from the controller 90. Specifically, the receiver 71 acquires thevalues of a string of symbols decoded by the correlation operator 71 bduring the reception operation, as control information c2, and outputsthe acquired control information c2 to the controller 90.

The controller 90, which includes a microprocessor (MCU), is activatedupon the supply of a trigger signal EN from the receiver 71, andgenerates a transmission and reception schedule for various signals onthe basis of detection time t2 supplied from the receiver 71. Then, thecontroller 90 performs a process of generating control signals SWC basedon the generated transmission and reception schedule and supplying thegenerated control signals SWC to the switch 76, a process of controllingthe receiver 71 to receive command signals, and a process of controllingthe transmitter 75 on the basis of control information c2 supplied fromthe receiver 71. The process of controlling the transmitter 75 includesdetermining whether a long burst signal is to be sent or a burst signaland a data signal are to be sent on the basis of a received commandsignal, instructing the transmitter 75 to send a long burst signal or aburst signal if a long burst signal or a burst signal is to be sent, andacquiring data which it is instructed to send by control information c2and supplying the acquired data to the transmitter 75 if a data signalis to be sent. The data supplied to the transmitter 75 include datarepresenting a pen pressure detected by the pen pressure detectionsensor 23.

The transmitter 75 is a circuit that generates signals to be sent to thesensor controller 31 and supplies the generated signals to the electrode21, and includes a modulator 73 and a voltage boosting circuit 74.

The modulator 73 is a circuit that generates a carrier signal(rectangular-wave signal) having a predetermined frequency or afrequency controlled by the controller 90, and outputs the carriersignal as it is or after modulating it under the control of thecontroller 90. When a long burst signal or a burst signal is to be sent,the modulator 73 does not modulate the carrier signal and outputs thecarrier signal as it is, or modulates the carrier signal with a patternof known values shared with the sensor controller 31 and outputs themodulated carrier signal. In this manner, the modulator 73 outputs along burst signal prior to being boosted or a burst signal prior tobeing boosted. When a data signal is to be sent, the modulator 73modulates the carrier signal with data supplied from the controller 90(based on on/off keying (OOK), phase shift keying (PSK), or the like),and outputs the modulated signal obtained as a result. In this manner,the modulator 73 outputs a data signal prior to being boosted.

The voltage boosting circuit 74 boosts the voltage of output signalsfrom the modulator 73 to a certain amplitude, to thereby generate a longburst signal, a burst signal, and a data signal. The long burst signal,the burst signal, and the data signal that have been generated by thevoltage boosting circuit 74 are supplied via the switch 76 to theelectrode 21, from which they are transmitted into space.

The arrangements and the operation of the stylus 2 and the sensorcontroller 31 according to the present embodiment have been describedabove. Now, operation of the stylus 2 and the sensor controller 31 willbe described in detail below with reference to flowcharts of processingsequences.

FIG. 9 is a flowchart of an overall operation sequence of the sensorcontroller 31. As depicted in FIG. 9, the sensor controller 31 isarranged to repeat the same operation that includes four finger touchdetecting processes (steps S1 and S2) and four stylus detectingprocesses (step S3), in each time period Tr (e.g., 16.67 ms, which isthe reciprocal of 60 Hz) that is defined as the reciprocal of a displayrefresh rate of a display panel such as a liquid crystal display panelor the like. The finger touch detecting processes and the stylusdetecting processes are performed alternately. Each of the finger touchdetecting processes is continuously carried out over a time period Tf(e.g., 1500 μs), and each of the stylus detecting processes iscontinuously carried out over a time period Ts (e.g., 2500 μs). Fordetecting finger F, two finger touch detecting processes (step S1 andstep S2) that are performed discretely before and after a stylusdetecting process are carried out as a single finger touch positiondetecting unit.

FIG. 10 is a flowchart of a stylus detecting process carried out by thesensor controller 31. Although not depicted, the sensor controller 31stores therein a state flag that indicates its own states. The statesthat can be indicated by the state flag include a stylus undetected andpen trigger signal transmission waiting state (=0), a stylus undetectedand response to a pen trigger signal waiting state (=1), a stylusdetected and position underived state (=2), a stylus position derivedstate (=3). The sensor controller 31 initially refers to the state flag(step S10).

If the state flag referred to in step S10 represents “0,” then thesensor controller 31 sends a pen trigger signal over a predeterminedtime period T (e.g., 2500 μs which is the same as the time period Tsdepicted in FIG. 9) in step S11. Specifically, the sensor controller 31sends a repetition of a detection pattern c1 and a delimiter patternSTP. Having finished the continuous transmission of the pen triggersignal, the sensor controller 31 sets the state flag to “1” (step S12),after which control goes back to step S10.

If the state flag referred to in step S10 represents “1,” then thesensor controller 31 sends a command signal for instructing the stylus 2to send a long burst signal (first uplink signal) (step S13). Thetransmission of various command signals including this command signaltakes at most a time period T0 (e.g., 200 μs) as depicted in FIG. 10.Thereafter, the sensor controller 31 performs a detecting operation todetect a long burst signal depicted in FIG. 10 over a time period T1(step S14). This detecting operation is performed in the first half ofthe full-range scanning process (first scan) described with reference toFIG. 7(a).

When the time period T1 has elapsed and the detecting operation todetect a long burst signal is finished, the sensor controller 31determines whether it has received a long burst signal or not (stepS15). If the sensor controller 31 determines that it has not received along burst signal as a result, then it sets the state flag to “0” (stepS16), after which control goes back to step S10. Step S16 represents aprocess in which the sensor controller 31 fails to detect downlinksignals for the reason that the stylus 2 is outside the sensing range SRdepicted in FIG. 1, for example. If the sensor controller 31 determinesthat it has received a long burst signal in step S15, then it sets thestate flag to “2” (step S17) and determines a command to be sent to thestylus (step S18), after which control goes back to step S10. Thecommand that is determined here is a command that instructs the stylus 2to send a long burst signal.

If the state flag referred to in step S10 represents “2,” then thesensor controller 31 again sends a command signal (first uplink signal)that instructs the stylus 2 to send a long burst signal (requesting LB)(step S19). Thereafter, the sensor controller 31 again performs adetecting operation to receive a long burst signal over a time period T1(step S20). This detecting operation is performed in the latter half ofthe full-range scanning process (first scan) described with reference toFIG. 7(b). When the operation of the first half of the full-rangescanning process (step S14) and the operation of the latter half of thefull-range scanning process (step S20) can be carried out in one timeperiod T1, these two steps S14 and S20 may be performed in one process.

When the time period T1 has elapsed and the detecting operation todetect a long burst signal is finished, the sensor controller 31determines whether it has received a long burst signal or not (stepS21). If the sensor controller 31 determines that it has not received along burst signal as a result, then it sets the state flag to “0” (stepS22), after which control goes back to step S10. Step S22 represents aprocess in which the sensor controller 31 fails to detect downlinksignals for the reason that the stylus 2 has left the sensing range SRdepicted in FIG. 1, for example. If the sensor controller 31 determinesthat it has received a long burst signal in step S21, then it sets thestate flag to “3” (step S23) and derives the position of the stylus 2 onthe basis of the result of the detection of the long burst signal instep S14 and the result of the detection of the long burst signal instep S20 (step S24). The sensor controller 31 then determines a commandto be sent to the stylus (step S25), after which control goes back tostep S10. The command that is determined here is a command thatinstructs the stylus 2 to send various data (stylus ID, datarepresenting a pen pressure, etc.). The command also serves to instructthe stylus 2 to send a burst signal over a time period T2.

If the state flag referred to in step S10 represents “3,” then thesensor controller 31 sends a command signal (second uplink signal)representing a command determined in step S25 or step S32 to bedescribed later (step S26). Thereafter, the sensor controller 31successively performs a detecting operation to detect a burst signalover a time period T2 shorter than the time period T1 (step S27). If thesensor controller 31 detects a burst signal, then it derives positionalcoordinates of the stylus 2 on the basis of the detected intensities atthe linear electrodes 30X, 30Y (step S28). The detecting operation todetect a burst signal in step S27 is performed according to the sectorscanning process (second scan) described with reference to FIG. 7(c).

When the time period T2 has elapsed and the detecting operation todetect a long burst signal is finished, the sensor controller 31performs a detecting operation to detect a data signal (step S29). Thisdetecting operation includes a decoding process for decoding a datasignal. The detecting operation to detect a data signal is carried outusing one linear electrode 30X or linear electrode 30Y selected on thebasis of the positional coordinates derived in preceding step S28. Inthis manner, it is possible to utilize the time period for detecting adata signal to the fullest, so that the sensor controller 31 can receivemore data from the stylus 2.

Having finished the detecting operation to detect a data signal, thesensor controller 31 determines whether it has received a burst signalor a data signal or not (step S30). If the sensor controller 31determines that it has not received either of them as a result, it setsthe state flag to “0” (step S31), after which control returns to stepS10. Step S31 represents a process in which the sensor controller 31fails to detect downlink signals for the reason that the stylus 2 hasleft the sensing range SR depicted in FIG. 1, for example. If the sensorcontroller 31 determines that it has received either one of them in stepS30, then the sensor controller 31 determines a command to be sent tothe stylus 2 (step S32), and then lets control return to step S10. Thecommand that is determined here is a command that instructs the stylus 2to send various data (stylus ID, data representing a pen pressure,etc.). The command also serves to instruct the stylus 2 to send a burstsignal over a time period T2.

FIG. 11 is a flowchart of an operation sequence of the stylus 2 whichcorresponds to FIG. 10. Although not depicted, the stylus 2 also storestherein a state flag that indicates its own states. The states that canbe indicated by the state flag include a sensor controller undetectedstate (=0) and a sensor controller detected state (=1). First, thestylus 2 refers to the state flag (step S40).

If the state flag referred to in step S40 represents “0,” then thestylus 2 enters a reception operation disabled state (step S41). After apredetermined time period has elapsed, the stylus 2 tries to detect adetection pattern c1 described above (step S42). The disabled period isprovided in step S41 in order to reduce the electric power consumed bythe stylus 2 by intermittently performing the detecting operation todetect a detection pattern c1.

Then, the stylus 2 determines whether a detection pattern c1 has beendetected by the detecting operation tried in step S42 (step S43). If thestylus 2 determines that a detection pattern c1 has not been detected asa result, then control goes back to step S40. If the stylus 2 determinesthat a detection pattern c1 has been detected, then the stylus 2continues a detecting operation to detect symbols of a detection patternc1 and a delimiter pattern STP until a delimiter pattern STP is detected(step S44). If a delimiter pattern STP is detected, then the stylus 2performs a process of synchronizing with the sensor controller 31 on thebasis of the detection time (step S45), and sets the state flag to “1”(step S46), after which control goes back to step S40. Specifically, thesynchronizing process in step S45 is a process of generating atransmission and reception schedule with the controller 90 depicted inFIG. 8.

If the state flag referred to in step S40 represents “1,” then thestylus 2 performs a detecting operation to detect a command signal (stepS47). The detecting operation is carried out over a time period T0.Then, the stylus 2 determines whether a command signal has been detectedby the detecting operation or not in step S47, and, if a command signalhas been detected, identifies the content indicated by the commandsignal (step S48). If the controller 90 determines that a command signalhas not been detected, then the stylus 2 sets the state flag to “0”(step S49), after which control goes back to step S40. Step S49represents a process in which the stylus 2 fails to detect uplinksignals for the reason that the stylus 2 has moved out of the sensingrange SR depicted in FIG. 1, for example.

If the stylus 2 determines that a command signal has been detected whichrepresents a command to send a long burst signal in step S48, then thestylus 2 determines to transmit a long burst signal and performs aprocess of sending a long burst signal over a time period T1 (step S50).Specifically, the stylus 2 continuously sends the signal having thepredetermined waveform described above that makes up a long burst signalover a time period T1. Thereafter, control goes back to step S40.

If the stylus 2 determines that a command signal has been detected whichrepresents a command to send data in step S48, then the stylus 2determines to transmit a burst signal and performs a process of sendinga burst signal over a time period T2 (step S51). Specifically, thestylus 2 continuously sends the signal having the predetermined waveformdescribed above that makes up a burst signal over a time period T2.Then, the stylus 2 performs a process of sending a data signal includingthe instructed data (step S52). Thereafter, control goes back to stepS40.

According to the present embodiment, as described above, in a stylusundetected state where the possibility that the stylus 2 is hovering ishigh, the sensor controller 31 can expect the stylus 2 to send a longburst signal which continues for a longer period of time than a normalburst signal. Consequently, while the time period of the detectingoperation per linear electrode is made longer than when a normal burstsignal is received, it is possible to scan more linear electrodes (inthe present embodiment, all the linear electrodes 30Y or the linearelectrodes 30X) within the time period of continuous transmission of along burst signal, for the purpose of detecting a burst signal. Thepossibility that the sensor controller 31 may fail to detect a burstsignal can be reduced while ensuring that the sensor controller 31 iscapable of detecting a burst signal over a wide range in the touchsurface.

According to the present disclosure, furthermore, since the full-rangescanning process is used for receiving a long burst signal, the timeperiod of the detecting operation per linear electrode is furtherincreased while ensuring that the sensor controller 31 is capable ofdetecting a burst signal over the entire the touch surface.

According to the present disclosure, moreover, since the sensorcontroller 31 instructs the stylus 2 to send a long burst signal basedon a command signal that instructs the stylus 2 to send a long burstsignal, the stylus 2 is clearly aware of a timing to send a long burstsignal.

Although the preferred embodiment of the present disclosure has beendescribed above, the present disclosure is not limited to the embodimentat all, but can be reduced to practice in various forms withoutdeparting from the scope thereof.

First through sixth modifications of the above embodiment will bedescribed below.

FIG. 12 is a diagram depicting an arrangement of a stylus 2 according toa first modification of the above embodiment. A sensor controller 31 andthe stylus 2 according to the present modification are different fromthose of the above embodiment in that they use, for transmission ofuplink signals, wireless communication protocols not based on thecapacitive coupling principle. The stylus 2 is different from that ofthe above embodiment in that it supports the transmission of two kindsof downlink signals DS1 and DS2 whose carrier signals are of differenttypes from each other. Both the downlink signals DS1 and DS2 are capableof sending a long burst signal, a burst signal, and data signal asdescribed above. The stylus 2 selectively uses the downlink signals DS1and DS2 depending on the kind of the sensor controller 31 which is inclose proximity thereto. The arrangement of the stylus 2 according tothe present modification will be described in detail below withreference to FIG. 12.

As depicted in FIG. 12, the stylus 2 according to the presentmodification has an electrode 21, a signal processor 24, a power supply25, an amplifier 26, and a receiver 27.

The receiver 27 is a functional section capable of performingcommunication based on Bluetooth® (registered trademark) as wirelesscommunication. According to the present modification, the receiver 27receives an uplink signal that the sensor controller 31 has sent basedon Bluetooth® (registered trademark).

The signal processor 24 is a functional section having a function toselectively send the two kinds of downlink signals DS1, DS2 and afunction to receive an uplink signal US via the receiver 27.Specifically, the signal processor 24 has a controller 91, a voltagebooster 92, an oscillator 93, and a switch 94.

The voltage booster 92 has a function to boost a DC voltage suppliedfrom the power supply 25, generating a DC voltage V1. According to aspecific example, the voltage booster 92 includes a DC-DC converter or acharge pump circuit.

The oscillator 93 has a function to perform an oscillating operationbased on the DC voltage supplied from the power supply 25 to generate anunmodulated sine-wave signal (carrier signal) that oscillates at apredetermined frequency. The amplifier 26 has a function to amplify thesine-wave signal generated by the oscillator 93 with a predeterminedamplification factor, generating an unmodulated sine-wave signal v2. Asdepicted in FIG. 12, the amplifier 26 should preferably include amamplifying circuit made up of a transformer and capacitors.

The switch 94, which includes a one-circuit three-contact switchelement, has a terminal “a” connected to the output terminal of thevoltage booster 92, a terminal “b” connected to the output terminal ofthe amplifier 26, a terminal “g” connected to a power supply line thatis supplied with a ground potential, and a common terminal c connectedto the electrode 21.

The controller 91 is an integrated circuit (IC) for supplying a controlsignal Ctrl that controls the switch 94 and controlling the receiver 27to receive an uplink signal sent by the sensor controller 31. Thecontroller 91 operates with electric power supplied from the powersupply 25. According to a specific example, the controller 91 may be anapplication specific integrated circuit (ASIC) or an MCU. The controller91 determines which one of the downlink signal DS1 and the downlinksignal DS2 is used to send a long burst signal, a burst signal, and adata signal on the basis of the content of an uplink signal received viathe receiver 27 or the fact that no uplink signal is received (in thecase where the sensor controller 31 supports only unidirectionalcommunication from the stylus 2 to the sensor controller 31). As withthe controller 90 depicted in FIG. 8, the controller 91 also determinesa transmission and reception schedule for various signals, etc., andcontrols the switch 94 based on the determined transmission andreception schedule.

For sending the downlink signal DS1, the controller 91 controls theswitch 94 to function as a first switch provided between the outputterminal of the voltage booster 92 and the electrode 21. Specifically,the controller 91 controls the switch 94 to switch between a state inwhich the terminal “a” is connected to the common terminal “c” and astate in which the terminal “g” is connected to the common terminal “c.”The state in which the terminal “a” is connected to the common terminal“c” corresponds to a state in which the first switch is on, and thestate in which the terminal “g” is connected to the common terminal “c”corresponds to a state in which the first switch is off.

For sending a burst signal or a long burst signal using the downlinksignal DS1, the controller 91 controls the switch 94 to performswitching operations periodically in predetermined periodic cycles. Whenthe terminal “a” is connected to the common terminal “c,” the DC voltageV1 comes through as the output voltage of the switch 94. When theterminal “g” is connected to the common terminal “c,” the groundpotential comes through as the output voltage of the switch 94.Consequently, the switch 94 outputs an unmodulated pulse train signalthat serves as a long burst signal or a burst signal.

For sending a data signal using the downlink signal DS1, the controller91 controls the switch 94 to perform a switching operation depending ondata, such as a pen pressure level P or switch information SW indicatingwhether a side switch (not depicted) on the stylus 2 is on or off. Thedata may include other information such as a stylus ID (identifyinginformation of the stylus 2), etc. The controller 91 generates a datasignal which is a pulse train signal modulated with data, by controllingthe switch 94 to perform switching operations in this manner. Specificmethods of modulating a pulse train signal by the controller 91 mayinclude on-off modulation and frequency modulation.

For sending the downlink signal DS2, the controller 91 controls theswitch 94 to function as a second switch provided between the outputterminal of the amplifier 26 and the electrode 21. Specifically, thecontroller 91 controls the switch 94 to switch between a state in whichthe terminal “b” is connected to the common terminal “c” and a state inwhich the terminal “g” is connected to the common terminal “c.” Thestate in which the terminal “b” is connected to the common terminal “c”corresponds to a state in which the second switch is on, and the statein which the terminal “g” is connected to the common terminal “c”corresponds to a state in which the second switch is off.

For sending a burst signal or a long burst signal using the downlinksignal DS2, the controller 91 controls the switch 94 to connect thecommon terminal “c” securely to the terminal “b.” Therefore, the switch94 outputs the unmodulated sine-wave signal v2 that serves as a longburst signal or a burst signal.

For sending a data signal using the downlink signal DS2, the controller91 controls the switch 94 to perform a switching operation depending ondata, such as pen pressure data P or switch information SW. It should benoted that, also in this case, the data may include other informationsuch as a stylus ID. The controller 91 generates a data signal which isa pulse train signal modulated with data, by thus controlling the switch94 to perform switching operations in this manner. A specific method ofmodulating a sine-wave signal by the controller 91 may include on-offmodulation.

According to the present modification, as described above, Bluetooth®(registered trademark) can be used to send and receive an uplink signal.Although the example using Bluetooth® (registered trademark) has beendescribed above, proximity wireless communications other than Bluetooth®(registered trademark) may be used to send and receive an uplink signal.

According to the present modification, the stylus 2 is capable ofperforming bidirectional or unidirectional communication between itselfand a plurality of different types of sensor controllers 31 byselectively using the downlink signals DS1 and DS2.

FIG. 13 is a flowchart of an operation sequence of a stylus 2 accordingto a second modification of the above embodiment. The stylus 2 accordingto the present modification is different from the stylus 2 according tothe above embodiment in that the stylus 2 according to the presentmodification sends a long burst signal immediately after it receives anyuplink signal while it is not detecting the sensor controller 31, and inthat it determines whether to send a burst signal immediately prior to adata signal. Details of operation of the stylus 2 according to thepresent modification will be described below with reference to FIG. 13.

As depicted in FIG. 13, the stylus 2 according to the presentmodification initially performs a detecting operation to detect anuplink signal (step S60). The stylus 2 determines whether an uplinksignal has been detected by the detecting operation or not (step S61).If the stylus 2 determines that an uplink signal has not been detected,then control goes back to step S60 to repeat the detecting operation. Ifthe stylus 2 determines that an uplink signal has been detected, thenthe stylus 2 sends a long burst signal without waiting for a commandsignal (step S62). Specifically, the stylus 2 sends signal having thepredetermined waveform described above over a time period T1.

After having sent the long burst signal, the stylus 2 carries out adetecting operation to detect a command signal (step S63). Then, thestylus 2 determines whether a command signal that instructs the stylus 2to send a data signal has been detected or not (step S64). If the stylus2 determines that the command signal has not been detected, then controlgoes back to step S62 to repeat the transmission of a long burst signal.If the stylus 2 determines that the command signal has been detected,then the stylus 2 determines whether it is to send a burst signal or not(step S65). The stylus 2 should preferably make this determination basedon the content of the detected command signal. In this manner, it ispossible for the sensor controller 31 to control the stylus 2 to send aburst signal or not.

A process to be carried out if the stylus 2 determines that it is tosend a burst signal in step S65 is the same as steps S51 and S52depicted in FIG. 11. Specifically, the stylus 2 sends a burst signal bysending the signal having the predetermined waveform over a time periodT2 (step S66), and sends a data signal including data instructed by thecommand signal detected in step S63 over a subsequent time period T1−T2(step S67). If the stylus 2 determines that it is not to send a burstsignal in step S65, then the stylus 2 sends a data signal including datainstructed by the command signal detected in step S63 over a time periodT1 (step S68).

After having sent the data signal in step S67 or step S68, the stylus 2lets control return to step S63. The stylus 2 is thus continuously ableto send data as instructed by the sensor controller 31.

According to the present modification, as described above, the stylus 2can send a long burst signal without waiting for a command signalincluding a command that instructs the stylus 2 to send a long burstsignal. Therefore, the stylus 2 can send a long burst signal to a sensorcontroller 31 that does not particularly support long burst signals.

Since the stylus 2 determines whether a burst signal is to be sentimmediately prior to a data signal, if the sensor controller 31 does notrequire the stylus 2 to send a burst signal, the stylus 2 can send adata signal over a longer time period (i.e., can send more data), andthe sensor controller 31 can acquire more data.

FIG. 14 is a flowchart of an operation sequence of a sensor controller31 according to a third modification of the above embodiment. The sensorcontroller 31 according to the present modification is different fromthe stylus 2 according to the above embodiment in that the sensorcontroller 31 sends a pen trigger signal in the first stylus detectingprocess (step S3 in FIG. 9) or sends a command signal for instructingthe stylus 2 to send a long burst signal subsequently to the executionof the first half of the full-range scanning process. Details ofoperation of the sensor controller 31 according to the presentmodification will be described below with reference to FIG. 14.

As depicted in FIG. 14, if the state flag referred to in step S10represents “0,” then the sensor controller 31 according to the presentmodification sends a pen trigger signal over a time period shorter thanthe example depicted in FIG. 10 (specifically, a time period T1) (stepS71). Then, the sensor controller 31 sends a command signal (firstuplink signal) for instructing the stylus 2 to send a long burst signal(step S72). Then, the sensor controller 31 sets the state flag to “1”(step S12), after which control goes back to step S10.

If the state flag referred to in step S10 represents “1,” then thesensor controller 31 according to the present modification performs adetecting operation to detect a long burst signal over a time period T1(step S73), and thereafter again sends a command signal (first uplinksignal) for instructing the stylus 2 to send a long burst signal (stepS74). The operation sequence is the same as step S14 depicted in FIG. 10in that the detecting operation in step S73 is carried out in the firsthalf of the full-range scanning process, but comparison between theoperation sequence and the example depicted in FIG. 10 indicates thatthe detecting operation to detect a long burst signal and thetransmission of a command signal are in reverse order.

If the state flag referred to in step S10 represents “2,” then thesensor controller 31 according to the present modification performs adetecting operation to detect a long burst signal over a time period T(step S75). The operation sequence is the same as step S14 depicted inFIG. 10 in that the detecting operation in step S73 is carried out inthe latter half of the full-range scanning process, but it will beunderstood from comparison between FIGS. 10 and 14 that the entire timeperiod T can be used for the detecting operation to detect a long burstsignal. The subsequent process is the same as the example depicted inFIG. 10, and its detailed description will be omitted.

In the present modification, the command sent in steps S72 and S74 forinstructing the stylus 2 to send a long burst signal should preferablyinclude information representing a time period of continuoustransmission of a long burst signal. The stylus 2 should preferablycontrol its time period of continuous transmission of a long burstsignal depending on the time period of continuous transmissionrepresented by the information. In this fashion, it is possible toequalize the period of time during which the sensor controller 31performs the detecting operation to detect a long burst signal and theperiod of time during which the stylus 2 sends a long burst signal.

According to the present modification, as described above, the latterhalf of the full-range scanning process can be carried out over a longertime period compared with the above embodiment. Therefore, the receptiontime per linear electrode 30X can further be increased, allowing thesensor controller 31 to receive a burst signal further reliably comparedwith the above embodiment.

FIG. 15 is a diagram depicting a long burst signal sent by a stylus 2according to a fourth modification of the above embodiment. A sensorcontroller 31 and a stylus 2 according to the present modification aredifferent from those of the above embodiment with respect to the formatof a long burst signal. The format of a long burst signal according tothe present modification will be described in detail below withreference to FIG. 15.

As depicted in FIG. 15, the long burst signal according to the presentmodification has a pattern in which a signal having a frequency f1(first frequency) and a signal having a frequency f2 (second frequency)different from the frequency f1 are successively arranged. Specifically,the long burst signal includes a first part having the frequency f1 anda latter part having the frequency f2.

If the long burst signal has a single frequency throughout its entireinterval, then the sensor controller 31 is unable to obtain anyinformation from the received long burst signal. As a consequence, thereis a possibility that the sensor controller 31 will mistake mere whitenoise or frequency-selective noise having a strong component near thefrequency f1 of a long burst signal. According to the long burst signalin the present modification, however, the sensor controller 31 is ableto determine that the received signal is a long burst signal due to thefact that the two kinds of frequencies are detected in a known sequence.According to the present modification, therefore, the possibility thatthe sensor controller 31 will operate by mistaking a signal which is nota long burst signal for a long burst signal can be lowered.

According to the present embodiment, the full-range scanning process fordetecting a long burst signal is carried out such that the odd-numberedlinear electrodes 30Y are scanned first and the even-numbered linearelectrodes 30Y are scanned subsequently. The full-range scanning processis carried out in this way in order for the sensor controller 31 to beable to receive both the first and second half portions of a long burstsignal. If the time period T1 of a long burst signal is sufficientlylong, then the sensor controller 31 may successively scan all the linearelectrodes 30Y at the frequency f1 and then successively scan again allthe linear electrodes 30Y at the frequency f2.

According to the present modification, as described above, thepossibility that the sensor controller 31 will operate by mistaking asignal which is not a long burst signal for a long burst signal can belowered.

In the present modification, the example has been described in which along burst signal is configured such that its first and second halfportions have different frequencies. However, a long burst signal mayhave any features insofar as they allow the sensor controller 31 todistinguish between white noise and a long burst signal. For example, along burst signal may be a signal in which L frequencies are varied in agiven sequence that has been determined in advance with respect to thesensor controller 31. In this case, the sensor controller 31 may scan Nlinear electrodes 30Y (or the M linear electrodes 30X) repeatedly Ltimes while varying the frequencies.

FIG. 16 is a flowchart of an operation sequence of a stylus 2 accordingto a fifth modification of the above embodiment. A sensor controller 31and a stylus 2 according to the present modification are different fromthose of the above embodiment in that the stylus 2 determines that thesensor controller 31 has not yet detected the stylus 2 on the basis ofan uplink signal. Details of operation of the stylus 2 according to thepresent modification will be described below with reference to FIG. 16.

As depicted in FIG. 16, the stylus 2 according to the presentmodification initially enters a sleep state (step S80). The sleep stateis the same as the reception operation disabled state (step S41)depicted in FIG. 11.

After a predetermined time period has elapsed in the sleep state, thestylus 2 performs a detecting operation to detect an uplink signal (stepS81). The stylus 2 determines whether an uplink signal has been detectedin the detecting operation or not (step S82). If the stylus 2 determinesthat an uplink signal has not been detected, then control goes back tostep S80 in which the stylus 2 enters a sleep state again. If the stylus2 determines that an uplink signal has been detected, then the stylus 2determines whether the uplink signal indicates that the sensorcontroller 31 has not yet detected the stylus 2 (it is in an undetectedstate) (step S83). In the stylus 2 depicted in FIG. 8, the controller 90carries out this determining process. In the stylus 2 depicted in FIG.12, the controller 91 carries out this determining process.

Specific processes of the determination in step S83 include thefollowing processes, for example. The first process applies in asituation where the sensor controller 31 explicitly sends an uplinksignal indicating that it has not detected the stylus 2. In this case,the stylus 2 may carry out the determination in step S83 on the basis ofwhether it has received the uplink signal. The second process applies ina situation where, as described in the above embodiment, the sensorcontroller 31 sends a command signal for instructing the stylus 2 tosend a long burst signal. As described above with reference to FIG. 10,the sensor controller 31 sends a command signal for instructing thestylus 2 to send a long burst signal when the sensor controller 31 hasnot yet detected by the stylus 2. In this case, therefore, the stylus 2may carry out the determination in step S83 on the basis of whether ithas received a command signal for instructing the stylus 2 to send along burst signal or not.

If the result of the determination is affirmative in step S83, then thestylus 2 sends a long burst signal (step S84). Specifically, the stylus2 sends the signal having the predetermined waveform described aboveover a time period T1. The long burst signal that is sent may be thelong burst signal depicted in FIG. 15 (a signal having a feature capableof distinguishing between white noise and a long burst signal).

If the result of the determination is negative in step S83, then thestylus 2 determines whether it is to send a burst signal or not (stepS85). A subsequent process (steps S85 through S88) is the same as theprocess of steps S65 through S68 illustrated in FIG. 13, and will not bedescribed in detail below.

According to the present modification, as described above, the stylus 2determines whether the sensor controller 31 has detected the stylus 2 ornot, and is able to determine that it is to send a long burst signal, aburst signal, and a data signal (or it is to send only a data signal) onthe basis of the result of the determination.

FIG. 17 is a diagram illustrative of a specific position excludingprocess according to a sixth modification of the above embodiment. FIG.18 is a flowchart of an operation sequence of a sensor controller 31according to the sixth modification of the present embodiment. Thepresent modification serves to remove those of one or more positions ofthe stylus 2 that have been derived as the result of the stylusdetecting process (step S3 in FIG. 9) which are positioned in fingertouch areas (information representing areas touched by finger F depictedin FIG. 1) detected by the finger touch detecting process (steps S1 andS2 in FIG. 9). The present modification will be described in detailbelow.

FIG. 17(a) depicts finger touch areas A1 and A2 detected by the fingertouch detecting process and FIG. 17(b) depicts positions B1 through B3of the stylus 2 derived by the stylus detecting process carried outimmediately after the finger touch detecting process in FIG. 17(a).

The finger touch areas A1 and A2 in FIG. 17(a) are detected because partof the electric current that flows through the linear electrodes of thesensor 30 flows toward the human body via a capacitive coupling betweenfinger F and the linear electrodes 30X and 30Y, as described above. InFIG. 17(a), the area of the finger touch area A1 is much larger than thearea of the finger touch area A2. The finger touch area A1 having such alarge area is normally formed when the palm or first of a hand, ratherthan a finger, is held in contact with the touch surface. Normally, thefinger touch area A1 is invalidated by another process (palm rejectionprocess) based on the size of the area. FIG. 17(a) depicts a statebefore A1 is invalidated.

The positions B1 through B3 of the stylus 2 depicted in FIG. 17(b) arederived on the basis of the detected intensities of a burst signal atthe linear electrodes 30X and 30Y in step S20 depicted in FIG. 10, forexample. A burst signal that reaches the sensor 30 (see FIG. 2) includesa component that comes directly from the electrode 21 (see FIGS. 8 and12) of the stylus 2 and, in addition, components that come via the handthe carries the stylus 2 and the other hand. Of the three positions B1through B3 detected in FIG. 17(b), only the position B3 has been derivedfrom the component that has come directly from the electrode 21 of thestylus 2 to the sensor 30, and the other two positions have been derivedfrom the components that have come to the sensor 30 via the hand thecarries the stylus 2 and the other hand.

Referring back to FIG. 17(a), it will be understood that the fingertouch areas A1 and A2 are detected at substantially the same positionsas the positions B1 and B2. The reason for this is that the positions B1and B2 are detected because a hand is close to the touch surface and thehand can be detected by the finger touch detecting process. The sensorcontroller 31 according to the present modification uses such arelationship between the finger touch areas and the stylus positions.The positions B1 and B2 are removed (excluded) from the positions B1through B3 of the stylus 2 that have been derived by the stylusdetecting process by referring to the result of the finger touchdetecting process. Details of operation of the sensor controller 31 forexcluding those positions will be described below with reference to FIG.18.

As depicted in FIG. 18, the sensor controller 31 initially detectsfinger touch areas (step S90). This detection process is performed inthe finger touch detecting process (steps S1 and S2) depicted in FIG. 9.

Thereafter, control goes to the stylus detecting process (step S3)depicted in FIG. 9, in which the sensor controller 31 acquires one ormore position candidates for the stylus 2 in the process indicated bystep S20 depicted in FIG. 10 (step S91). The sensor controller 31 thenacquires one or more finger touch areas detected in step S90 (step S92).Providing the above palm rejection process is carried out, the fingertouch areas that are thus acquired have yet to undergo the palmrejection process.

Then, the sensor controller 31 repeats the process subsequent to stepS94 on each of the position candidates for the stylus 2 that have beenacquired in step S91. Specifically, the sensor controller 31 determineswhether the position represented by each position candidate is includedin either one of the one or more finger touch areas acquired in step S92(step S94). If the sensor controller 31 determines that the position isnot included, then the sensor controller 31 recognizes the positionrepresented by the position candidate as the position of the stylus 2,and performs a normal process (step S95). If the sensor controller 31determines that the position is included, then the sensor controller 31invalidates the position candidate (step S96). The invalidated positioncandidate will not be used as at least the position of the stylus 2 in asubsequent process. The invalidating process may be realized by notoutputting the position of the stylus 2 from the sensor controller 31 tothe system controller of the electronic device 3 or by outputting theposition of the stylus 2 and using a flag or the like to indicate thatthe position is an invalid area.

According to the present modification, as described above, the sensorcontroller 31 can remove a position derived from a component of a burstsignal that has come to the sensor 30 via a hand carrying the stylus 2or the other hand, from a plurality of positions of the stylus 2 derivedby the stylus detecting process.

In the above embodiment, the full-range scanning process has beendescribed as being carried out using all of the N linear electrodes 30Yand the M linear electrodes 30X. In the full-range scanning process, itis sufficient to perform a larger scan (a scan using many linearelectrodes) than the sector scan, and it is not necessary to use all ofthe N linear electrodes 30Y and the M linear electrodes 30X. In otherwords, the full-range scanning process may be performed using adetection area in a first range which covers the touch surface wholly orpartly, and the sector scan may be performed using a detection area in arange selected within the first range. In this case, a command signal (acommand signal for instructing the stylus 2 to send a long burst signal)prior to the full-range scanning process may be sent from the firstrange, and a command signal (a command signal for instructing the stylus2 to send a burst signal and a data signal) prior to the sector scan maybe sent from the selected range.

In the above embodiment, the scanning process that successively uses theN linear electrodes 30Y (first half) and the scanning process thatsuccessively uses the M linear electrodes 30X (latter half) areseparately described as representing operation of the full-rangescanning process. If the time period T1 of continuous transmission of along burst signal is sufficiently long, then the position(two-dimensional coordinate position) of the stylus 2 may be specifiedusing the linear electrodes 30X after operating the linear electrodes30Y.

In the above embodiment, the example has been described in which a datasignal is not sent after a long burst signal has been sent. However, adata signal may be sent subsequently to a long burst signal. The timeperiod of continuous transmission of a data signal in this case may beshorter than the time period of continuous transmission of a burstsignal and a data signal depicted in FIG. 3. This data signal issuitable for the transmission of data that can be represented by ashorter number of bits than a pen pressure or the like, such as anon/off state of a switch mounted on a casing of the stylus 2.

DESCRIPTION OF REFERENCE SYMBOLS

2: Stylus

3: Electronic device

21: Electrode

23: Pen pressure detection sensor

24: Signal processor

25: Power supply

26: Amplifier

27: Receiver

30: Sensor

30X, 30Y: Linear electrode

31: Sensor controller

40: Selector

41 x, 41 y: Conductor selecting circuit

50: Receiver

51: Amplifying circuit

52: Detecting circuit

53: Converter

60: Transmitter

61: Pattern supply

62: Switch

63: Spreading processor

64: Code train holder

65: Transmission guard

70: Logic unit

71 a: Waveform regenerator

71 b: Correlation operator

73: Modulator

74: Voltage boosting circuit

75: Transmitter

76: Switch

90: Controller

91: Controller

92: Voltage booster

93: Oscillator

94: Switch

A1, A2: Finger touch area

B1-B3: Stylus position

DS1, DS2: Downlink signal

EN: Trigger signal

F: Finger

P: Pen pressure data

Res: Data

SR: Sensing range

SW: Switch information

US: Uplink signal

The invention claimed is:
 1. A stylus capable of bidirectionallycommunicating with a sensor controller, comprising: a receiver thatreceives an uplink signal sent by the sensor controller; a controller,which, in response to a data of the uplink signal indicating a requestfor a data signal, determines to send a normal burst signal, which has apredetermined pattern that is known in advance between the stylus andthe sensor controller, over a second time period T2; and in response toa data of the uplink signal indicating a request for a long burst signalhaving the predetermined pattern and used to identify a position of thestylus, determines to send the long burst signal over a first timeperiod T1 longer than the second time period T2; and a transmitter thatsends the normal burst signal or the long burst signal on the basis of aresult of the determination to send the normal burst signal or the longburst signal, respectively, by the controller.
 2. The stylus accordingto claim 1, wherein when the controller determines to send the normalburst signal, the transmitter transmits the data signal in a time periodcorresponding to a difference between the second time period T2 and thefirst time period T1.
 3. The stylus according to claim 1, wherein thedata of the uplink signal varies depending on whether the sensorcontroller has detected or not detected a presence or position of thestylus, and when the data of the uplink signal indicates that the sensorcontroller has not detected the presence or position of the stylus, thecontroller determines to send the long burst signal.
 4. The stylusaccording to claim 1, wherein the controller determines whether to sendthe normal burst signal or the long burst signal, irrespective of astate of the stylus being either a hover state or a contact state. 5.The stylus according to claim 1, wherein the normal burst signal and thelong burst signal having the predetermined pattern have a predeterminedfrequency.
 6. A stylus capable of bidirectionally communicating with asensor controller, comprising: a receiver that receives an uplink signalsent by the sensor controller; a controller that determines a state ofthe sensor controller based on the uplink signal; and a transmitter,which, in response to the controller determining, based on the uplinksignal, that the sensor controller has not detected the stylus,continuously sends a long burst signal used to identify a position ofthe stylus and having a predetermined pattern that is known in advancebetween the stylus and the sensor controller over a predetermined timeperiod, and in response to the controller determining, based on theuplink signal, that the sensor controller has derived a position of thestylus, sends a data signal indicative of an operation state of thestylus, rather than continuously sending the long burst signal havingthe predetermined pattern over the predetermined time period.
 7. Thestylus according to claim 6, wherein the predetermined pattern is apattern including a series of a signal having a first frequency and asignal having a second frequency different from the first frequency. 8.The stylus according to claim 6, wherein, in response to the controllerdetermining, based on the uplink signal, that the sensor controller hasderived the position of the stylus, the transmitter continuously sends asignal having the predetermined pattern over a time period shorter thanthe predetermined time period and sends the data signal.
 9. The stylusaccording to claim 6, wherein the operation state of the stylus is a penpressure level sensed by a pressure sensor.
 10. The stylus according toclaim 6, wherein the transmitter determines whether to send the longburst signal or the data signal, irrespective of a state of the stylusbeing either a hover state or a contact state.
 11. The stylus accordingto claim 6, wherein the long burst signal having the predeterminedpattern has a predetermined frequency.